This invention relates to a seat used for a vehicle such as, for example, a shovel car, a tractor and the like.
FIG. 5 shows one example of a conventional seat of a vehicle. This seat includes a pair of frames (an upper frame and a lower frame) 1, 2 disposed vertically away from each other, and a pair of links 3, 4 of an X-shape disposed between the upper frame 1 and the lower frame 2. Those links 3, 4 are rotatably connected to each other at their intermediate parts. The front end portions of the links 3, 4 are slidably connected to the frames 1, 2, and the rear end portions thereof are rotatably connected to the frames 1, 2. Owing to the foregoing arrangement, the upper frame 1 can make a vertical movement between an uppermost position indicated by a solid line of FIG. 5 and a lowermost position indicated by an imaginary line of FIG. 5 while maintaining its parallel posture with respect to the lower frame 2. A front end portion of the suspension spring 5 is connected to the link 3, and a rear end portion of the spring 5 is connected to the upper frame 1. Owing to the foregoing arrangement, the link 3 is biased in the rising direction, thereby supporting the upper frame 1 elastically. The spring force of the suspension spring 5 is adjusted such that the frame 1 is located at an intermediate position between the uppermost position and the lowermost position, under the condition that a passenger sits on a cushion 6 which is placed on the upper frame 1. When vibration of the vehicle is transmitted to the seat, the links 3, 4 are rotated and the suspension spring 5 is expanded/contracted, thereby absorbing the vibration.
As shown in FIG. 6, it has heretofore been demanded for a vehicle seat to increase the thickness of the cushion 6 and to enlarge the space in the cabin by reducing, as much as possible, the distance between the upper frame 1 and the lower frame 2 in the uppermost position. However, if this demand should be satisfied, the links 3, 4 would be greatly folded and therefore, the suspension spring 5 would be merely slightly expanded/contracted with respect to rotation of the link 3 and the increasing/decreasing amount of the spring force would be small. Accordingly, only with a slight variation of the external force, the upper frame 1 would reach the uppermost or lowermost position, thus providing a shock. Accordingly, the passenger""s sitting comfort is degraded.
The present invention has been made in view of the above situation. It is, therefore, an object of the present invention to provide a seat of a vehicle in which vibration absorbing capability of a suspension spring can be obtained sufficiently even if a distance between frames is reduced.
In order to achieve the above object, the features of the present invention reside in a seat of a vehicle comprising (A) a pair of frames disposed vertically away from each other; (B) a parallel maintaining mechanism including a first link and a second link which are rotatably connected to each other at intermediate parts thereof to form an X-shape, the first link being slidably connected at an upper end portion thereof to an upper frame and rotatably connected at a lower end portion thereof to a lower frame, the second link being rotatably connected at an upper end portion thereof to the upper frame and slidably connected at a lower end portion thereof to the lower frame; (C) a slide member slidably disposed at one of the upper frame and the lower frame; (D) a suspension spring extending along the one frame, one end portion of the suspension spring being connected to the one frame and the other end portion being connected to the slide member; and (E) cam means disposed between one of the first link and the second link and the slide member and adapted to convert rotation of the link into sliding movement of the slide member and hence into expansion/contraction of the suspension spring; the suspension spring biasing the one link in a rising direction through the slide member and cam means, thereby supporting the upper frame. Owing to the foregoing construction, by making the folding angle of the link in the uppermost position, the distance between the upper frame and the lower frame can be reduced, the cushion can be increased in thickness and the cabin can be enlarged in space. Moreover, since the expanding/contracting amount of the suspension spring can be increased by the cam means, the vibration transmitted to the seat can fully be absorbed, and an enhanced riding comfort can be obtained.
It is preferred that the cam means includes an abutment member disposed at the one link, and an inclination cam face formed on the slide member and brought into abutment with the abutment member by the suspension spring. Owing to the foregoing arrangement, the construction of the cam means can be simplified.
Preferably, the cam face becomes gentle in gradation towards the one frame. Owing to the foregoing arrangement, the upper frame can be restrained from lowering and the bottom touching feel can surely be prevented.
It is preferred that the first and second links and the slide member are slid in a back and forth direction and the suspension spring is extended in a back and forth direction. Owing to the foregoing arrangement, the seat can be made compact.
Preferably, a pair of the first and second links and a pair of the cam means are provided on each of left and right side portions of the frame, a slide member is extended leftwards and rightwards, and opposite end portions of the slide member are connected to the one link through the cam means. Owing to the foregoing arrangement, the left and right links and the suspension spring can be connected through only one slide member and a reliable cam action can be obtained with a simple construction.